Method and system for performing chemical mechanical polishing

ABSTRACT

A method of using a polishing system includes securing a wafer in a carrier head, the carrier head including a housing enclosing the wafer, in which the housing includes a retainer ring recess and a retainer ring positioned in the retainer ring recess, the retainer ring surrounding the wafer, in which the retainer ring includes a main body portion and a bottom portion connected to the main body portion, and a bottom surface of the bottom portion includes at least one first engraved region and a first non-engraved region adjacent to the first engraved region; pressing the wafer against a polishing pad; and moving the carrier head or the polishing pad relative to the other.

This application is a Continuation Application of U.S. application Ser.No. 16/259,856, filed Jan. 28, 2019, which is herein incorporated byreference in its entirety.

BACKGROUND

Integrated circuits may be formed using various photolithographictechniques. Such techniques typically include use of a ChemicalMechanical Polishing (CMP) process, which is performed to polish asurface of a wafer. However, conventional CMP processes may have waferscratch issues, which can lead to wafer acceptance test failure or lowwafer yields.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a cross-sectional view of a carrier head over a polishing padin accordance with some embodiments.

FIG. 2 shows a region R1 in FIG. 1 , which is a partially enlargedcross-sectional view of the top surface of the polishing pad in whichdebris and abrasive particles accumulated thereon, in accordance withsome embodiments.

FIG. 3 illustrates a bottom view of a retainer ring in accordance withsome embodiments.

FIG. 4A shows a region R2 in FIG. 3 , which is a partially enlargedcross-sectional view of the retainer ring, in accordance with someembodiments.

FIG. 4B shows a region R2′ similar to the region R2 in FIG. 3 , which isa partially enlarged cross-sectional view of the retainer ring, inaccordance with some other embodiments.

FIG. 5 is a partially enlarged cross-sectional view of the retainer ringshown in FIG. 3 in accordance with some other embodiments.

FIGS. 6A-6D are portions of an engraved region of a bottom portion ofthe retainer ring with various geometric shapes in accordance with someembodiments.

FIG. 7 is a cross-sectional view of a carrier head and a conditioningdisk over a polishing pad in accordance with some embodiments.

FIGS. 8A-8E are portions of an engraved region of a bottom portion ofthe conditioning disk with various geometric shapes in accordance withsome embodiments.

FIGS. 9A-9C illustrate a bottom surface of the conditioning disk in FIG.7 in accordance with some embodiments.

FIG. 10 is a flow chart showing an illustrative method for using a CMPprocess on a wafer in accordance with some embodiments.

FIGS. 11 and 12 illustrate schematic perspective views of a CMP processcorresponding to the flow chart in FIG. 10 in accordance with someembodiments.

FIG. 13 is a flow chart showing an illustrative method for using a CMPprocess on a wafer.

FIGS. 14-16 illustrate schematic perspective views of a CMP processcorresponding to the flow chart in FIG. 13 in accordance with someembodiments.

FIG. 17 is a schematic diagram of a laser processing apparatus inaccordance with some embodiments.

FIG. 18 is a perspective view of a superfine processing machine inaccordance with some embodiments.

FIGS. 19-25 illustrate perspective views and cross-sectional views ofintermediate stages in the formation of a Fin Field-Effect Transistors(FinFET) in accordance with some embodiments.

FIGS. 26-30 illustrate perspective views and cross-sectional views ofintermediate stages in the formation of FinFETs in accordance with someembodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

A Chemical Mechanical Polishing (CMP) system is provided in accordancewith various exemplary embodiments. The variations of some embodimentsare discussed. Throughout the various views and illustrativeembodiments, like reference numbers are used to designate like elements.The embodiments of the present disclosure also include the scope ofusing the CMP system in accordance with the embodiments to manufactureintegrated circuits. For Example, the CMP system is used to planarizewafers, in which integrated circuits are formed.

FIG. 1 is a cross-sectional view of a carrier head 104 over a polishingpad 106 in accordance with some embodiments. FIG. 2 shows a region R1 inFIG. 1 , which is a partially enlarged cross-sectional view of a topsurface 106 a of the polishing pad 106 in which debris 122 andby-product residues 118 (e.g., residues of abrasive particles of slurry)resulting from the CMP process accumulated thereon. Reference is made toFIGS. 1 and 2 . A carrier head 102 is usable in a polishing system, suchas a CMP system 194 and 202 depicted in FIGS. 11-16 vide infra. A wafer104 is secured in the carrier head 102 and between the carrier head 102and a polishing pad 106. In some embodiments, the wafer 104 containsactive devices. In some embodiments, the wafer 104 contains passivedevices. In some embodiments, the wafer 104 is a raw un-processed wafer104. In some embodiments, the carrier head 102 is configured to move thewafer 104 relative to the polishing pad 106.

The carrier head 102 includes a housing 108, a membrane support 110, amembrane 112, and a retainer ring 114. The housing 108 is configured toenclose a membrane support 110 and the wafer 104 and hold the wafer 104against the polishing pad 106. The housing 108 is capable of moving in adirection perpendicular to a polishing surface (e.g., a top surface 106a) of polishing pad 106 during the polishing process.

The membrane support 110 has one or more ports defined therein. In someembodiments, the membrane support 110 is solid. In some embodiments, themembrane support 110 is a substantially rigid material, such as a metal,a dielectric material, or another suitable material. The membrane 112 issecured to the membrane support 110 and is configured to press the wafer104 against the polishing pad 106. The membrane 112 has a lower surfaceconfigured to be in contact with the wafer 104. In some embodiments, themembrane 112 and the membrane support 110 form one or more chambers 116.The membrane 112 is used to increase uniformity of the pressure appliedto the wafer 104 during the polishing process. Pressures of the chambers116 are set by fluid or air provided through corresponding ports inorder to shape or maintain a predetermined surface profile at the lowersurface of the membrane 112. As a result, pressure applied to the wafer104 is controlled to be evenly distributed throughout the entire wafer104. In some embodiments, the membrane 112 is formed of a flexible andelastic fluid-impermeable material. In some embodiments, the membrane112 includes at least one of neoprene, chloroprene, ethylene propylenerubber, silicone, or other suitable flexible materials. In someembodiments, the membrane support 110 is omitted, and the housing 108directly provides support for the membrane 112.

The housing 108 includes a material having sufficient mechanicalstrength to withstand the pressure exerted during the polishing process.The housing 108 has a diameter sufficiently large to enclose the wafer104 and the retainer ring 114 surrounding the wafer 104. The housing 108includes a retainer ring recess 117 in a periphery region of the housing108 to accommodate the retainer ring 114. In other words, the retainerring 114 is positioned in the retainer ring recess 117. In someembodiments, the housing 108 is rotatable in a plane parallel to thepolishing surface 106 a of the polishing pad 106. In some embodiments,the housing 108 is pivotable about an axis Z1 perpendicular to thepolishing surface 106 a of the polishing pad 106.

The polishing pad 106 is used to remove materials from the wafer 104. Insome embodiments, during a polishing process, the retainer ring 114 andthe wafer 104 are in contact with the polishing pad 106. In someembodiments, a slurry (e.g., a slurry 198 shown in FIG. 11 ) isdispensed on the polishing pad 106 during the polishing process. Theslurry may include a chemical solution (such as surfactant or wettingagent) and a plurality of abrasive particles in the chemical solution.In some embodiments, the polishing pad 106 is movable relative to thewafer 104. In some embodiments, the top surface 106 a of the polishingpad 106 is a grooved surface (see FIG. 2 ) and includes grooves 120,whereby the grooved surface is configured to face a to-be polishedsurface of the wafer 104. Such a grooved surface may advantageouslyprovide a variety of functions such as, for example, preventing ahydroplaning effect between the polishing pad 106 and the wafer 104,acting as drain channels for removing polishing debris 122, and ensuringdispensed slurry to be uniformly distributed across the polishing pad106, etc.

It is not uncommon to have polishing debris 122 remaining on the topsurface 106 a of the polishing pad 106 during or after a polishingprocess. Such debris 122 may be formed due to a variety of reasons suchas, for example, debris 122 that is polished out from the wafer 104 andnot drained through the grooves 120. As illustrated, the debris 122 andby-product residues 118 (e.g., residues of abrasive particles of slurry)may block the dispensed slurry from going into the groove 120. As aresults, the debris 122 and the abrasive particles 118 are generallyconsidered as defects to the wafer 104 since the debris 122 may induceremoval rate (RR) vibration due to insufficient slurry utilization andmay cause dishing (e.g., the pattern loading effect) and defects (e.g.,surface scratches, residues, etc). Conventionally, such debris 122(defect) is removed offline and manually, which means that the debris122 is usually identified by a user/administrator of the polishing pad106 after one or more polishing processes, and then a conditioningdevice (e.g., a conditioning disk) may be used to remove the debris 122though the user/administrator applying a downward force.

The retainer ring 114 is configured to reduce lateral movement of thewafer 104 with respect to the carrier head 102 during the polishingprocess. The retainer ring 114 includes a main body portion 124 and abottom portion 126 connected to the main body portion 124. In someembodiments, the main body portion 124 has a continuous annular shape.The retainer ring 114 is attached to the retainer ring recess 117through the main body portion 124 of the retainer ring 114. The mainbody portion 124 includes an inner periphery 124 a configured tosurround the wafer 104, an outer periphery 124 b, and a bottom surface124 c connecting the inner periphery 124 a and the outer periphery 124b. The bottom portion 126 is attached to the bottom surface 124 c of themain body portion 124. The bottom portion 126 has at least one engravedregion 128 (see FIGS. 4A, 4B, and 5) formed on a bottom surface 126 a ofthe bottom portion 126 facing the polishing pad 106 using anultra-precision machining method, for example, a method using a laserprocessing apparatus or a superfine processing machine. The bottomportion 126 further includes a non-engraved region 129 (see FIGS. 4A,4B, and 5 ) adjacent to and surrounding the engraved region 128. Thenon-engraved region 129 is a substantially flat region. Flatness of thenon-engraved region 129 is greater than flatness of the engraved region128. Stated differently, roughness of the engraved region 128 is greaterthan roughness of the non-engraved region 129. The engraved region 128of the bottom portion 126 of the retainer ring 114 can help dislodge thedebris 122 and the abrasive particles 118 trapped in the polishing pad106 when the polishing pad 106 and the carrier head 102 are operated topolish the wafer 104 at a predetermined removal rate to refresh the topsurface 106 a of the polishing pad 106. In other words, the polishingpad 106 can polish the wafer 104, while simultaneously beingreconditioned by the engraved region 128 of the bottom portion 126 ofthe retainer ring 114. In some embodiments, the engraved region 128 ofthe bottom portion 126 of the retainer ring 114 contacts the top surface106 a of the polishing pad 106 when the polishing pad 106 is to beconditioned. During the conditioning, both the polishing pad 106 and theretainer ring 114 rotate, so that the engraved region 128 of the bottomportion 126 of the retainer ring 114 moves relatively to the top surface106 a of the polishing pad 106, and hence polishing and re-texturizingthe top surface 106 a of the polishing pad 106. As a result, thepolishing pad 106 is conditioned and capable of holding dispensedslurry. Therefore, the wafer 104 can be effectively polished and thepolishing pad 106 can be reconditioned in real-time during polishing thewafer 104 without disposing a conditioning disk, which can be costly,thereby saving production cost and time.

In some embodiments, a first vacuum system 130 is coupled to the carrierhead 102. The first vacuum system 130 includes a first vacuum port 132,e.g., a plurality of first vacuum holes 152 disposed on the non-engravedregion 129 of the bottom portion 126 of the retainer ring 114 (see FIGS.4A, 4B, and 5 ). The first vacuum port 132 is connected to a firstvacuum pump 134. The first vacuum pump 134 is controlled by acontroller, such as a first controller 136. The first vacuum system 130is configured to apply vacuum suction force through the first vacuumport 132 to the top surface 106 a of the polishing pad 106 in adirection away from the top surface 106 a to remove materials (e.g.,debris 122, abrasive particles 118, etc.) on the top surface 106 a ofthe polishing pad 106.

In operation, the first vacuum port 132 can be placed above a selectedlocation on the polishing pad 106 or in direct contact with thepolishing pad 106 at the location. The first vacuum pump 134 is turnedon such that the first vacuum system 130 applies suction with a pressurein a direction away from the top surface 106 a of the polishing pad 106.In other words, the pressure in a space between the first vacuum port132 and the top surface 106 a of the polishing pad 106 is lower than theatmospheric pressure in which the polishing system is situated. As aresult, materials, such as polishing detritus including debris 122,abrasive particles 118, and cleaning fluid, on the top surface 106 a ofthe polishing pad 106 and in the space between the first vacuum port 132and the top surface 106 a of the polishing pad 106 are drawn into thefirst vacuum system 130. In some embodiments, the main body portion 124and the bottom portion 126 of the retainer ring 114 includesubstantially the same material, for example, non-diamond material, suchas high strength thermosetting polymer (e.g., poly-ether ketone (PEEK),polyaryletherketone (PAEK), polytetrafluoroethylene (PTFE),polyphenylene sulfide (PPS), etc.), metal, ceramic, the like, orcombinations thereof. Therefore, conditioning the polishing pad 106using such engraved region 128 may help save production cost.

The carrier head 102 further includes one or more cushion members 138 inthe retainer ring recess 117, as shown in FIG. 1 . The one or morecushion members 138 are configured to press the retainer ring 114against the polishing pad 106 and to adjust position of the retainerring 114 by adjusting corresponding pressures of the cushion members138. In some embodiments, the cushion members 138 each include aflexible element enclosing the chamber 116 for containing a fluid. Insome embodiments, the cushion members 138 include a flexible solidmaterial. In some embodiments, the cushion members 138 are omitted, andthe retainer ring 114 is directly attached to the retainer ring recess117.

FIG. 3 illustrates a bottom view of the retainer ring shown in FIG. 1 inaccordance with some embodiments. A plurality of grooves 150 are formedin a bottom surface of the bottom portion 126 of the retainer ring 114.The grooves 150 create openings extending from an outer perimeter of theretainer ring 114 to the wafer 104, thus facilitating a flow (e.g.,allowing for the even distribution) of the slurry over the wafer 104. Itis contemplated in other embodiments to have grooves with differentdimensions.

FIG. 4A shows a region R2 in FIG. 3 , which is a partially enlargedcross-sectional view of the retainer ring 114, in accordance with someembodiments. The bottom portion 126 of the retainer ring 114 includes atleast one engraved region 128 and a non-engraved region 129 adjacent toand surrounding the engraved region 128. In other words, the engravedregion 128 and the non-engraved region 129 combine to form the bottomsurface 126 a of the bottom portion 126 of the retainer ring 114. Thebottom portion 126 of the retainer ring 114 further includes at leastone first vacuum hole 152 formed on the non-engraved region 129 of thebottom portion 126 of the retainer ring 114. The engraved region 128 andthe first vacuum hole 152 may be arranged randomly on the bottom portion126. As compared to a carrier head 102 without the first vacuum system130, the conditioning process with the first vacuum system 130 can beperformed more efficiently and the throughput of the process can beimproved; and the wafer 104 polished by the engraved region 128 of thebottom portion 126 of the retainer ring 114 can have reduced defectscaused by the polishing detritus remaining on the top surface 106 a ofthe polishing pad 106 after the conditioning.

FIG. 4B shows a region R2′ similar to the region R2 in FIG. 4A, exceptfor a second engraved region 131 formed on the bottom surface 124 c ofthe main body portion 124 exposed by and between the grooves 150 inaccordance with some other embodiments. The bottom surface 124 c of themain body portion 124 includes a second non-engraved region 133 adjacentto and surrounding the second engraved region 131. The second engravedregions 131 can also help dislodge the debris 122 trapped in thepolishing pad 106 to refresh the top surface 106 a of the polishing pad106. However, it is understood that the number of the first vacuum hole152 is only for illustration purposes and are not limiting.

FIG. 5 is a partially enlarged cross-sectional view of the retainer ring114 shown in FIG. 3 . In some embodiments, chamfers 154 are formed at atop surface 126 b and a side surface 126 c of the bottom portion 126. Inother words, the bottom portion 126 has at least one rounded corner(e.g., the chamfer 154). The chamfers 154 are used for enhancingconditioning the polishing pad 106, for example, removing theaccumulated debris 122, abrasive particles 118, and byproducts duringthe CMP polishing process and also making the top surface 106 a of thepolishing pad 106 rough.

FIGS. 6A-6D illustrate the engraved region of the bottom portion of theretainer ring with various geometric shapes of FIG. 1 in accordance withsome embodiments. Reference is made to FIG. 6A. The engraved region 128has multiple pyramid-shaped protrusions 156 and grooves 158 cut into orformed in the bottom surface 126 a of the bottom portion 126. Eachprotrusion 156 has four sides 160 and a plateau 162. A network of theintersecting perpendicular grooves 158 separate adjacent protrusions 156from each other. Each protrusion 156 may have a dimension of a lengthL1×width W1×height H1 of from about 0.2×0.2×0.2 (mm) to about 10×10×1(mm) in some embodiments. The protrusions 156 are equally spaced apartfrom the grooves 158. FIG. 6B shows an engraved region 128 a withanother kind of geometric shape similar to the engraved region 128,except for each protrusion 156 a includes four sides 160 a which meet atan apex 166. Each protrusion 156 a may have a dimension of a lengthL2×width W2×height H2 of from about 0.2×0.2×0.2 (mm) to about 10×10×1(mm) in some embodiments. Reference is made to FIG. 6C. FIG. 6C shows anengraved region 128 b with another kind of geometric shape similar tothe engraved region 128, except for each protrusion 156 b may becube-shaped in some embodiments. Each protrusion 156 b may have adimension D1 in a range from about 0.2 mm to about 10 mm in someembodiments. Reference is made to FIG. 6D. FIG. 6D shows an engravedregion 128 c with another kind of geometric shape similar to theengraved region 128, except for each protrusion 156 c may becylinder-shaped in some embodiments. Each protrusion 156 c has adiameter D2 in a range from about 0.2 mm to about 10 mm in someembodiments. If the dimensions of the abovementioned protrusions 156-156c are out of the above-selected ranges, the abrasive particles 118 andthe debris 122 may not be effectively removed from the polishing pad106. In some embodiments, the dimensions of the abovementionedprotrusions 156-156 c are less than a width of the retainer ring 114. Insome embodiments, the protrusions 156-156 c and the non-engraved region129 (see FIGS. 4A, 4B, and 5 ), which is a substantially flat region,are monolithic. In other words, the protrusions 156-156 c and thenon-engraved region 129 (see FIGS. 4A, 4B, and 5), which is asubstantially flat region, are one-piece formed.

FIG. 7 is a cross-sectional view of a carrier head and a conditioningdisk over a polishing pad in accordance with some embodiments. Aconditioning disk 140 is placed on the top surface 106 a of thepolishing pad 106 in some other embodiments. The conditioning disk 140includes at least one engraved region 142 disposed on a bottom surface140 a of the conditioning disk 140 facing the top surface 106 a of thepolishing pad 106. The engraved region 142 of the conditioning disk 140may be formed using an ultra-precision machining method, for example, amethod using a laser processing apparatus or a superfine processingmachine. The conditioning disk 140 further includes a non-engravedregion 143 (see FIGS. 9A-9C) disposed on the bottom surface 140 a of theconditioning disk 140 which is adjacent to the engraved region 142 insome embodiments. In other words, the non-engraved region 143 is asubstantially flat region. Flatness of the non-engraved region 143 isgreater than flatness of the engraved region 142. Stated differently,roughness of the engraved region 142 is greater than roughness of thenon-engraved region 143. The engraved region 142 and the non-engravedregion 143 combine to form the bottom surface 140 a of the conditioningdisk 140. The engraved region 142 of the conditioning disk 140 can helpdislodge the debris 122 and the abrasive particles 118 trapped in thepolishing pad 106 to refresh the top surface 106 a of the polishing pad106. As a result, the polishing pad 106 is conditioned and capable ofholding newly provided slurry.

A second vacuum system 144 is coupled to the conditioning disk 140. Thesecond vacuum system 144 includes a second vacuum port 146, e.g., aplurality of holes formed in the side of the conditioning disk 140 (seeFIGS. 9A-9C). The second vacuum port 146 is connected to a second vacuumpump 148. The second vacuum pump 148 is controlled by a controller, suchas a second controller 151. The second vacuum system 144 is configuredto apply suction through the second vacuum port 146 to the top surface106 a of the polishing pad 106 in a direction away from the top surface106 a to draw removable materials (e.g., debris 122, abrasive particles118, etc.) from the top surface 106 a of the polishing pad 106.

In operation, the second vacuum port 146 can be placed above a selectedlocation on the polishing pad 106 or in direct contact with thepolishing pad 106 at the location. The second vacuum pump 148 is runsuch that the second vacuum system 144 applies vacuum suction force witha pressure in a direction away from the top surface 106 a of thepolishing pad 106. In other words, the pressure in a space between thesecond vacuum port 146 and the top surface 106 a of the polishing pad106 is lower than the atmospheric pressure in which the polishing systemis situated. As a result, materials, such as polishing detritusincluding debris 122, abrasive particles 118, and cleaning fluid, on thetop surface 106 a of the polishing pad 106 and in the space between thesecond vacuum port 146 and the top surface 106 a of the polishing pad106 are drawn into the second vacuum system 144.

In some embodiments, the engraved region 142 of the conditioning disk140 contacts the top surface 106 a of the polishing pad 106 when thepolishing pad 106 is to be conditioned. During the conditioning, boththe polishing pad 106 and the conditioning disk 140 rotate, so that theengraved region 142 of the conditioning disk 140 moves relatively to thetop surface 106 a of the polishing pad 106, and hence polishing andre-texturizing the top surface 106 a of the polishing pad 106. As aresult, the polishing pad 106 is conditioned and capable of holdingnewly provided slurry.

In some embodiments, the non-engraved region 143 and the engraved region142 of the conditioning disk 140 include substantially the samematerial, for example, non-diamond material, such as high strengththermosetting polymer (e.g., poly-ether ketone (PEEK),polyaryletherketone (PAEK), polytetrafluoroethylene (PTFE),polyphenylene sulfide (PPS), etc.), metal, ceramic, the like, orcombinations thereof. Since such conditioning disk 140 may be costlycompared to a diamond material, production cost is saved.

The present disclosure provides various embodiments of systems andmethods to avoid the above-identified issue by providing an in-situ(during polishing) conditioning the polishing pad 106. The in-situconditioning may be implemented through the engraved region 128 on thebottom portion 126 of the retainer ring 114 facing the polishing pad 106coupled to the first vacuum system 130 and the engraved regions 142formed on the bottom surface 140 a of the conditioning disk 140 coupledto the second vacuum system 144, which will be described in thefollowing discussion.

FIGS. 8A-8E illustrate engraved regions on the bottom surface of theconditioning disk with various geometric shapes of FIG. 7 in accordancewith some embodiments. Reference is made to FIG. 8A. The engraved region142 has multiple pyramid-shaped protrusions 170 and grooves 172 cut intoor formed in the bottom surface 140 a of the conditioning disk 140. Eachprotrusion 170 has four sides 174 and a plateau 176. A network of theintersecting perpendicular grooves 172 separate adjacent protrusions 170from each other. Each protrusion 170 may have a dimension of a lengthL3×width W3×height H3 of from about 0.2×0.2×0.2 (mm) to about 10×10×1(mm) in some embodiments. FIG. 8B shows an engraved region 142 a withanother kind of geometric shape similar to the engraved region 142 ofthe conditioning disk 140 of FIG. 8A, except for each protrusion 170 a1includes four sides 174 a which meet at an apex 178. Each protrusion170 a may have a dimension of a length L4×width W4×height H4 of fromabout 0.2×0.2×0.2 (mm) to about 10×10×1 (mm) in some embodiments.Reference is made to FIG. 8C. FIG. 8C shows an engraved region 142 bwith another kind of geometric shape similar to the engraved region 128,except for each protrusion 170 b may be cube-shaped in some embodiments.Each protrusion may have a dimension D3 in a range from about 0.2 mm toabout 10 mm in some embodiments. Reference is made to FIG. 8D. FIG. 8Dshows an engraved region 142 c with another kind of geometric shapesimilar to the engraved region 142, except for each protrusion 170 c maybe cylinder-shaped in some embodiments. Each cylinder-shaped protrusionhas a diameter D4 in a range from about 0.2 mm to about 10 mm. Referenceis made to FIG. 8E. FIG. 8E shows an engraved region 142 d with anotherkind of geometric shape similar to the engraved region 128, except forthe each protrusion 170 d has a lower portion 180 with a uniform heightH5 in a range from about 0.2 mm to about 10 mm and an upper portion 182with four sides 184 which meet at an apex 186. If the dimensions of theabovementioned protrusions 170-170 d are out of the correspondingselected ranges, abrasive particles 118 and the debris 122 may not beeffectively removed from the polishing pad 106. In some embodiments, thedimensions of the abovementioned protrusions 170-170 d are less than awidth of the retainer ring 114.

FIGS. 9A-9C illustrate the bottom surface of the conditioning disk withvarious geometrical distribution in FIG. 7 in accordance with someembodiments. The engraved regions of the bottom surface of theconditioning disk may have various geometrical distributions, forexample, distributions shown in FIGS. 9A-9C. As shown in FIG. 9A, insome embodiments, the distribution of the engraved region 142 e of theconditioning disk 140 may be circular-shaped including a diameter D5ranging from about 5 inches to about 6 inches. The conditioning disk 140includes at least one second vacuum hole 188 formed on the bottomsurface 140 a of the conditioning disk 140. The second vacuum hole 188may be connected to a second vacuum pump 148 in order to reduce thepressure and generate at least a partial vacuum within the second vacuumhole 188 (see FIG. 7 ). FIG. 9B shows another conditioning disk 140 bsimilar to the conditioning disk 140, except for the positions of thesecond vacuum holes 188 a and the distribution of the engraved region142 f. In greater detail, in some embodiments, the distribution of theengraved region 142 f is donut-shaped including a ring-shaped portion190 that encloses a circular shape portion 192. The ring-shaped portion190 of the engraved region 142 f has a width W5 ranging from about 0.2inches to about 0.8 inches in some embodiments. The second vacuum hole188 a may be disposed between the ring-shaped portion 190 and thecircular shape portion 192. FIG. 9C shows another conditioning disk 140c similar to the conditioning disk 140, except for the positions of thesecond vacuum holes 188 b and the engraved region 142 g. In greaterdetail, in some embodiments, the distribution of the engraved region 142g is sector-shaped with a central angle α in radians. The central angleα of the sector-shaped engraved region 142 g may be an acute angle in arange from about 10 degrees to about 90 degrees. In some otherembodiments, the central angle α of the sector-shaped engraved region142 g may be an obtuse angle. The second vacuum holes 188 b may bedisposed between the engraved regions 142 g. However, it is understoodthat the number of the second vacuum holes 188-188 b is only forillustration purposes and are not limiting. In some embodiments, theprotrusions 170-170 d (see FIGS. 8A-8E) and the non-engraved region 143,which is a substantially flat region, are monolithic. In other words,the protrusions 170-170 d (see FIGS. 8A-8E) and the non-engraved region143, which is a substantially flat region, are one-piece formed.

FIG. 10 is a flow chart showing an illustrative method 1000 for using aCMP process on a wafer 104. Additional steps can be provided before,during, and after the method, and some of the steps described can bereplaced or eliminated for other embodiments of the method. FIGS. 11 and12 illustrate schematic perspective views of intermediate stages in theCMP process corresponding to the flow chart in FIG. 10 in accordancewith some embodiments.

As illustrated in FIG. 11 , a CMP system 194 includes a platen 196, apolishing pad 106 over the platen 196, a carrier head 102 over thepolishing pad 106, and a first vacuum system 130 coupled to the carrierhead 102. The to-be-polished wafer 104 is placed proximate to thepolishing pad 106. The first vacuum system 130 includes a first vacuumport 132, e.g., a plurality of first vacuum holes 152 disposed on thenon-engraved region 129 of the bottom portion 126 of the retainer ring114 (see FIGS. 4A, 4B, and 5 ). The first vacuum port 132 is connectedto a first vacuum pump 134. The first vacuum pump 134 is controlled bythe first controller 136. The method 1000 begins at block 1002 where aslurry is provided over the polishing pad. With reference to FIG. 11 ,in some embodiments of block 1002, a slurry 198 is dispensed by a slurrydispenser 200 over the polishing pad 106. The slurry dispenser 200 hasan outlet directly over the polishing pad 106 in order to dispense theslurry 198 onto the polishing pad 106. The slurry 198 includes areactive chemical solution that reacts with the surface layer of thewafer 104. Furthermore, the slurry includes abrasive particles (e.g.,abrasive particles 118 in FIG. 2 ) for mechanically polishing the wafer104.

Returning to FIG. 10 , the method 1000 then proceeds to block 1004 wherethe carrier head and the platen are rotated and the first vacuum systemis operated. With reference to FIG. 12 , in some embodiments of block1004, the carrier head 102 and the platen 196 are rotated and the firstvacuum system 130 is operated. In greater detail, the platen 196 isrotated by a mechanism (not shown), and hence the polishing pad 106fixed thereon is also rotated along with the platen 196. The wafer 104is pressed against the polishing pad 106, the carrier head 102 isrotated hence causes the rotation of the wafer 104 which is fixed ontothe carrier head 102, and the first vacuum pump 134 is run to apply thevacuum suction force. In some embodiments, applying the vacuum suctionforce and moving the carrier head 102 can be performed substantiallysynchronously. In some other embodiments, applying the vacuum suctionforce is performed after moving the carrier head 102. The carrier head102 moves relative to the polishing pad 106. The engraved region 128(see FIG. 1 ) of the bottom portion 126 of the retainer ring 114 is infriction engagement with the polishing pad 106 during moving the carrierhead 102 to condition the polishing pad 106. Therefore, the engravedregion 128 of the retainer ring 114 dislodges the debris 122 and theabrasive particles 118 trapped in the polishing pad 106. The firstvacuum pump 134 applies the vacuum suction force with a pressure in adirection away from the polishing pad 106 to refresh the top surface 106a of the polishing pad 106 through the first vacuum port 132 (e.g., thefirst vacuum holes 152 in FIGS. 4A, 4B and 5 ). In other words, thepressure in a space between the first vacuum port 132 and the topsurface 106 a of the polishing pad 106 is lower than the atmosphericpressure in which the CMP system 194 is situated. As a result, removablematerials, such as polishing detritus including the debris 122, theslurry 198 (e.g., abrasive particles 118), on the top surface 106 a ofthe polishing pad 106 and in the space between the first vacuum port 132and the top surface 106 a of the polishing pad 106 are drawn into andcollected by the first vacuum system 130 during the polishing process.In some embodiments, the carrier head 102 and the polishing pad 106rotate in the same direction (clockwise or counter-clockwise). Inaccordance with alternative embodiments, the carrier head 102 and thepolishing pad 106 rotate in opposite directions. The mechanism forrotating the carrier head 102 is not illustrated. With the rotation ofthe polishing pad 106 and the carrier head 102, the slurry 198 flowsbetween the wafer 104 and the polishing pad 106. Through the chemicalreaction between the reactive chemical solution in the slurry 198 andthe surface layer of the wafer 104, and further through the mechanicalpolishing, the surface layer of the wafer 104 is removed. Therefore, thewafer 104 can be effectively polished and the polishing pad 106 can bereconditioned substantially synchronously without disposing aconditioning disk, which can be costly, thereby saving production costand time.

Embodiments of the disclosure are not limited to the embodimentsmentioned above. FIG. 13 is a flow chart showing an illustrative method1300 for using a CMP process on the wafer 104 in accordance with anotherembodiment. Additional steps can be provided before, during, and afterthe method, and some of the steps described can be replaced oreliminated for other embodiments of the method. FIGS. 14-16 illustrateschematic perspective views of intermediate stages in the CMP processcorresponding to the flow chart in FIG. 13 in accordance with someembodiments.

As illustrated in FIG. 14 , a CMP system 202 is similar to the CMPsystem 194, except for a conditioning disk 140 over the polishing pad106 and a second vacuum system 144 coupled to the conditioning disk 140.The second vacuum system 144 includes a second vacuum port 146, e.g., aplurality of second vacuum holes 188 disposed on the non-engraved region143 of the bottom surface 140 a of the conditioning disk 140 (see FIGS.9A-9C). The method 1300 begins at block 1302 where a slurry is providedover the polishing pad. With reference to FIG. 14 , in some embodimentsof block 1302, a slurry 198 is dispensed by a slurry dispenser 200 overthe polishing pad 106. Since the slurry 198 is dispensed as discussedpreviously with regard to FIG. 11 , a detailed description of the sameis omitted herein for the sake of brevity.

Returning to FIG. 13 , the method 1300 then proceeds to block 1304 wherethe carrier head and the platen are rotated and the first vacuum systemis operated. With reference with FIG. 15 , in some embodiments of block1304, the carrier head 102 and the platen 196 are rotated and the firstvacuum system 130 is operated. Since the carrier head 102 and the platen196 are rotated and the first vacuum system 130 is operated as discussedpreviously with regard to FIG. 12 , a detailed description of the sameis omitted herein for the sake of brevity.

Returning to FIG. 13 , the method 1300 then proceeds to block 1306 wherea conditioning disk is rotated and a second vacuum system is operated.With reference to FIG. 16 , in some embodiments of block 1306, aconditioning disk 140 is rotated and a second vacuum system 144 isoperated. In greater detail, the polishing pad 106 is conditioned usingthe conditioning disk 140, in which the conditioning disk 140 is rotatedand the second vacuum pump 148 coupled to the conditioning disk 140 isrun such that the second vacuum pump 148 applies vacuum suction forcewith a pressure in a direction away from the polishing pad 106. Theengraved regions 142 formed on the bottom surface 140 a of theconditioning disk 140 can help dislodge the debris 122 and the abrasiveparticles 118 trapped in the polishing pad 106 to refresh the topsurface 106 a of the polishing pad 106. As a result, the polishing pad106 is conditioned and capable of holding newly provided slurry. In someembodiments, the conditioning using the conditioning disk 140 isperformed during the polishing the wafer 104. In other words, theconditioning the conditioning disk 140 and the polishing the wafer 104are performed substantially simultaneously. In some other embodiments,the conditioning using the conditioning disk 140 is performed after thepolishing the wafer 104.

As discussed previously, in some embodiments, the engraved regions 128of the bottom portion 126 of the retainer ring 114 and the engravedregions 142 on the bottom surface 140 a of the conditioning disk 140 maybe formed using an ultra-precision machining method, for example, amethod using a laser processing apparatus or a superfine processingmachine. FIG. 17 is a schematic diagram of a laser processing apparatusin accordance with some embodiments. As shown in FIG. 17 , a laserprocessing apparatus 204 includes a laser generator 206 generating alaser beam 208, a beam splitting optical system 210 for controlling thenumber of sub-laser beams 212 by dividing the laser beam 208 into aplurality of sub-laser beams 212, and a stage 214 to which a processingtarget 216 (e.g., the retainer ring 114 or the conditioning disk 140)processed with the laser beam 208 is mounted and controlling a locationof the processing target 216. The laser generator 206 may be a picosecond laser generator or a femto second-to-micro second lasergenerator. The sub-laser beams 212 generated by the laser generator 206can be focused to a spot size of from about 10 nm to about 20 μM.

FIG. 18 is a perspective view of a superfine processing machine 218 inaccordance with some embodiments which has therein an orthogonal,triaxial and movable stage and a rotating mechanism that rotates adiamond tool. In FIG. 18 , X-axis table 220 that is driven in the X-axisdirection and Z-axis table 222 that is driven in the Z-axis directionare mounted on a machine platen 224. On the X-axis table 220, there isfixed Y-axis stage 226 that is driven in the Y-axis direction, androtating mechanism 228 that rotates a diamond tool 230 is fixed on theY-axis stage 226. Its axis of rotation is in parallel with Z-axis.Further, a workpiece 232 (e.g., the retainer ring 114 or theconditioning disk 140) is clamped on the Z-axis table 222. A method ofcutting operation employing the superfine processing machine shown inFIG. 18 is a method wherein a transfer optical surface is created withan enveloping surface of a tool locus, when repeating actions to feedthe workpiece 232 slightly in the Z-axis direction by the Z-axis table222 after cutting by feeding in the X-axis direction by the X-axis table220, while rotating the diamond tool 230 at a high speed, and it is onecalled generally a fly cutting method. High speed processing can beconducted with less load on the point of a blade even when feeding inthe X-axis direction is increased.

FIGS. 19-25 illustrate perspective views and cross-sectional views ofintermediate stages in the formation of Fin Field-Effect Transistors(FinFETs) in accordance with some embodiments that involves a CMPprocess using the CMP tool as discussed previously. The fins may bepatterned by any suitable method. For example, the fins may be patternedusing one or more photolithography processes, includingdouble-patterning or multi-patterning processes. Generally,double-patterning or multi-patterning processes combine photolithographyand self-aligned processes, allowing patterns to be created that have,for example, pitches smaller than what is otherwise obtainable using asingle, direct photolithography process. For example, in one embodiment,a sacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers may then be used to pattern thefins.

FIG. 19 illustrates a perspective view of an initial structure. Theinitial structure includes a wafer 104 a, which further includes asubstrate 302. The substrate 302 may be a semiconductor substrate, whichmay be a silicon substrate, a silicon germanium substrate, or asubstrate formed of other semiconductor materials. In accordance withsome embodiments of the present disclosure, the substrate 302 includes abulk silicon substrate and an epitaxy silicon germanium (SiGe) layer ora germanium layer (without silicon therein) over the bulk siliconsubstrate. The substrate 302 may be doped with a p-type or an n-typeimpurity. Isolation regions 304 such as Shallow Trench Isolation (STI)regions may be formed to extend into the substrate 302. The portions ofthe substrate 302 between the neighboring STI regions 304 are referredto as semiconductor strips 306, which are in a device region 308. Thedevice region 308 is a p-type transistor region, in which a p-typetransistor such as a p-type FinFET is to be formed or an n-typetransistor region, in which an n-type transistor such as an n-typeFinFET is to be formed.

The STI regions 304 may include a liner oxide (not shown). The lineroxide may be formed of a thermal oxide formed through a thermaloxidation of a surface layer of the substrate 302. The liner oxide mayalso be a deposited silicon oxide layer formed using, for example,Atomic Layer Deposition (ALD), High-Density Plasma Chemical VaporDeposition (HDPCVD), or Chemical Vapor Deposition (CVD). The STI regions304 may also include a dielectric material over the liner oxide, and thedielectric material may be formed using Flowable Chemical VaporDeposition (FCVD), spin-on coating, or the like.

Referring to FIG. 20 , the STI regions 304 are recessed, so that the topportions of the semiconductor strips 306 protrude higher than a topsurfaces 304 a of the neighboring STI regions 304 to form protrudingfins 306′. The etching may be performed using a dry etching process,wherein NH₃ and NF₃ are used as the etching gases. During the etchingprocess, plasma may be generated. Argon may also be included. Inaccordance with alternative embodiments of the present disclosure, therecessing of the STI regions 304 is performed using a wet etch process.The etching chemical may include diluted HF, for example.

The materials of the protruding fins 306′ may also be replaced withmaterials different from that of the substrate 302. For example, theprotruding fins 306′ may be formed of an elementary (single element)semiconductor, such as silicon or germanium in a crystalline structure;a compound semiconductor, such as silicon germanium, silicon carbide,gallium arsenic, gallium phosphide, indium phosphide, indium arsenide,and/or indium antimonide; a non-semiconductor material, such assoda-lime glass, fused silica, fused quartz, and/or calcium fluoride(CaF₂); and/or combinations thereof.

Referring to FIG. 21 , dummy gate stacks 310 are formed on the topsurfaces and the sidewalls of protruding fins 306′. The dummy gatestacks 310 may include dummy gate dielectrics 312 and dummy gateelectrodes 314 over the dummy gate dielectrics 312. Dummy gateelectrodes 314 may be formed, for example, using polysilicon, and othermaterials may also be used. The dummy gate stacks 310 may also includeone (or a plurality of) hard mask layers 316. The hard mask layer 316may be formed of SiN, SiO, SiC, SiOC, SiON, SiCN, SiOCN, TiN, AlON,Al₂O₃, or the like. The dummy gate stacks 310 crosses over a single oneor a plurality of protruding fins 306′. The dummy gate stack 310 mayalso have lengthwise directions perpendicular to the lengthwisedirections of the respective protruding fins 306′.

Gate spacers 318 are formed on the sidewalls of the dummy gate stacks310. In the meantime, fin spacers (not shown) may also be formed on thesidewalls of protruding fins 306′. In accordance with some embodimentsof the present disclosure, gate spacers 318 are formed of anoxygen-containing dielectric material(s) such as silicon oxynitride(SiON), silicon oxy-carbo-nitride (SiOCN), silicon oxide (SiO₂), siliconoxy-carbide (SiOC), or the like. Non-oxygen-containing materials such assilicon nitride (SiN) and/or silicon carbide (SiC) may also be used toform gate spacers 318, depending on the formation method of thesubsequently formed inhibitor film. Gate spacers 318 may includeair-gaps, or may formed as including pores, and may have a single-layerstructure or a multi-layer structure including a plurality of dielectriclayers.

An etching step (referred to as source/drain recessing hereinafter) isthen performed to etch the portions of the protruding fins 306′ that arenot covered by the dummy gate stack 310 and the gate spacers 318. Therecessing may be anisotropic, and hence the portions of protruding fins306′ directly underlying the dummy gate stack 310 and the gate spacers318 are protected, and are not etched. The top surfaces 306 a of therecessed semiconductor strips 306 may be lower than the top surfaces 304a of the STI regions 304 in accordance with some embodiments. Recesses320 are accordingly formed between the STI regions 304. The recesses 320are located on opposite sides of the dummy gate stack 310. Next, epitaxyregions 322 (source/drain regions) are formed by selectively growing asemiconductor material in the recesses 320, resulting in the structurein FIG. 22 . In some other embodiments, some adjacent epitaxy regions322 may grow together to form a merged epitaxial structure. In someembodiments, the epitaxy regions 322 include silicon germanium orsilicon. Depending on whether the resulting FinFET is a p-type FinFET oran n-type FinFET, a p-type or an n-type impurity may be in-situ dopedwith the proceeding of the epitaxy. For example, when the resultingFinFET is a p-type FinFET, the epitaxy regions 322 may include SiGe,SiGeB, Ge, GeSn, or the like. In some cases, the epitaxy regions 322 ofan n-type FinFET may include silicon, SiC, SiCP, SiP, or the like. Insome embodiments of the present disclosure, the epitaxy regions 322comprise III-V compound semiconductors such as GaAs, InP, GaN, InGaAs,InAlAs, GaSb, AlSb, AlAs, AlP, GaP, combinations thereof, ormulti-layers thereof. After the recesses 320 are filled with the epitaxyregions 322, the further epitaxial growth of the epitaxy regions 322causes the epitaxy regions 322 to expand horizontally, and facets may beformed.

After the epitaxy step, the epitaxy regions 322 may be further implantedwith a p-type or an n-type impurity to form source and drain regions,which are also denoted using reference numeral 322. In some embodiments,the implantation step is skipped since the epitaxy regions 322 arein-situ doped with the p-type or n-type impurity during the epitaxy. Theepitaxy regions 322 include lower portions 322 a that are formed in theSTI regions 304, and upper portions 322 b that are formed over the topsurfaces 304 a of the STI regions 304. The lower portions 322 a, whosesidewalls are shaped by the shapes of the recesses 320 may have(substantially) straight edges, which may also be substantial verticaledges that are substantially perpendicular to the major surfaces ofsubstrate 302.

Contact Etch Stop Layer (CESL) 324 and Inter-Layer Dielectric (ILD) 326are then formed, as shown in FIG. 23A, which illustrate a perspectiveview. The CESL 324 may be formed of SiN, SiCN, SiOC, SiON, SiCN, SiOCN,or the like. In accordance with some embodiments of the presentdisclosure, the CESL 324 may include or may be free from oxygen therein.The CESL 324 may be formed using a conformal deposition method such asALD or CVD, for example. The ILD 236 may include a dielectric materialformed using, for example, FCVD, spin-on coating, CVD, or anotherdeposition method. The ILD 326 may also be formed of anoxygen-containing dielectric material, which may be silicon-oxide (SiO)based or silicon-oxycarbide (SiOC) based such as Tetra Ethyl OrthoSilicate (TEOS) oxide, Plasma-Enhanced CVD (PECVD) oxide (SiO₂),Phospho-Silicate Glass (PSG), Boro-Silicate Glass (BSG), Boron-DopedPhospho-Silicate Glass (BPSG), or the like. A slurry includes abrasiveparticles 118 is provided on the top surface 106 a of the polishing pad106 (see FIGS. 11 and 14 ) to polish the wafer 104 a (e.g., portions ofthe ILD 326, the dummy gate stacks 310, and the gate spacers 318). Theabrasive particles 118 schematically illustrated as over a top surfaceof the ILD 326 are not part of the wafer 104 a for illustrationpurposes. FIG. 23B shows a cross-sectional view obtained from thevertical plane containing line A-A in FIG. 23A.

A planarization step such as Chemical Mechanical Polish (CMP) ormechanical grinding using the CMP systems 194 and 202 shown in FIG. 1 or7 and the methods 1000 or 1300 shown in FIG. 10 or FIG. 13 may beperformed to level the top surfaces of the ILD 326, the dummy gatestacks 310, and the gate spacers 318 with each other, as shown in FIGS.24A and 24B. If the planarization step is performed without using theCMP system or methods as discussed previously, the ILD 326 would bedished, as shown in FIG. 24C. That is, some debris 122 and abrasiveparticles 118 may accumulate at an interface between the ILD 326 and thedummy gate stacks 310 and lead to a dishing effect on the ILD 326, theCESL 324, and the gate spacer 318.

After the CMP process, the dummy gate stack 310, which includes the hardmask layer 316, the dummy gate electrode 314 and the dummy gatedielectric 312, is replaced with a replacement gate stack 328, whichincludes a gate electrode 330 and a replacement gate dielectric 332 asshown in FIG. 25 .

When replacing the dummy gate stack 310, the hard mask layers 316, thedummy gate electrodes 314 and the dummy gate dielectrics 312 (FIGS. 24Aand 24B) are first removed in one or a plurality of etching steps,resulting in a trench (opening) to be formed between the gate spacers318. In the formation of the replacement gates, a gate dielectric 332(FIG. 25 ) is first formed, which extends into the recess left by theremoved dummy gate stack 310, and may have a portion extending over theILD 326. In accordance with some embodiments of the present disclosure,the gate dielectric 332 includes an Interfacial Layer (IL, not shownseparately) as its lower part. The IL may include an oxide layer such asa silicon oxide layer, which is formed through a chemical oxidationprocess or a deposition process. The gate dielectric 332 may alsoinclude a high-k dielectric layer formed over the IL. The high-kdielectric layer is formed as a conformal layer, and includes a high-kdielectric material such as hafnium oxide, lanthanum oxide, aluminumoxide, zirconium oxide, or the like. The dielectric constant (k-value)of the high-k dielectric material is higher than 3.9, and may be higherthan about 7.0. In accordance with some embodiments of the presentdisclosure, the high-k dielectric layer in the gate dielectric 332 isformed using ALD or CVD.

The gate electrode 330 is formed over the gate dielectric 332 andfilling the remaining portion of the recess. The formation of the gateelectrode 330 may include a plurality of deposition processes to deposita plurality of conductive layers, and performing a planarization step toremove the excess portions of the conductive layers over the ILD 326.The deposition of the conductive layers may be performed using conformaldeposition methods such as ALD or CVD.

The gate electrode 330 may include a diffusion barrier layer and awork-function layer (or a plurality of work-function layers) over thediffusion barrier layer. The diffusion barrier layer may be formed oftitanium nitride (TiN), which may (or may not) be doped with silicon toform TiSiN. The work-function layer determines the work function of thegate, and includes at least one layer, or a plurality of layers formedof different materials. The specific material of the work-function layeris selected according to whether the respective FinFET is an n-typeFinFET or a p-type FinFET. For example, for the n-type FinFET in then-type device region 308, the work-function layer may include a TaNlayer and a titanium aluminum (TiAl) layer over the TaN layer. For thep-type FinFET in the p-type device region 308, the work-function layermay include a TaN layer, a TiN layer over the TaN layer, and a TiAllayer over the TiN layer. After the deposition of the work-functionlayer(s), another barrier layer, which may be another TiN layer, isformed. The gate electrode 330 may also include a filling metal, whichmay be formed of tungsten or cobalt, for example. After the formation ofthe replacement gate stack 328, the replacement gate stack 328 is etchedback, and the dielectric hard mask 334 is formed over the etched-backreplacement gate stack 328.

Next, the ILD 326 and the CESL 324 are etched to form contact openings.The etching may be performed using, for example, Reactive Ion Etching(RIE). In a subsequent step, as shown in FIG. 25 , source/drain contactplugs 336 are formed. Before forming the contact plugs 336, the portionsof the CESL 324 exposed to the contact openings are first etched,revealing the epitaxy regions 322. The silicide regions 338 are thenformed on the epitaxy regions 322. In accordance with some embodimentsof the present disclosure, the contact plugs 336 include barrier layersand a metal-containing material over the respective barrier layers. Inaccordance with some embodiments of the present disclosure, theformation of the contact plugs 336 includes forming a blanket barrierlayer and a metal-containing material over the blanket barrier layer,and performing a planarization to remove excess portions of the blanketbarrier layer and the metal-containing material. The barrier layer maybe formed of a metal nitride such as titanium nitride or tantalumnitride. The metal-containing material may be formed of tungsten,cobalt, copper, or the like. An n-type or a p-type FinFET 308 is thusformed.

FIGS. 26-30 illustrate perspective views and cross-sectional views ofintermediate stages in the formation of Fin Field-Effect Transistors(FinFETs) which include a device region 308 a, (e.g., at least one shortchannel FinFET) and a device region 308 b (e.g., at least one longchannel FinFET) in accordance with some embodiments that use the method1000 or the method 1300 in the CMP process.

FIG. 26 illustrates a perspective view of an initial structure. Theinitial structure includes a wafer 104 b, which further includes asubstrate 302 where the short channel FinFET 308 a and the long channelFinFET 308 b are formed. Referring to FIG. 26 , the first dummy gatestacks 310′ and the second dummy gate stacks 310″ are formed on the topsurfaces and the sidewalls of protruding fins 306′. The first dummy gatestacks 310′ may include dummy gate dielectrics 312′ and dummy gateelectrodes 314 a′ over the dummy gate dielectrics 312′. The second dummygate stacks 310″ may include dummy gate dielectrics 312″ and dummy gateelectrodes 314″ over the dummy gate dielectrics 312″. A first width W6of the first dummy gate stack 310′ is smaller than a second width W7 ofthe second dummy gate stack 310″. A lengthwise direction of the firstand second dummy gate stacks 310′ and 310″ are perpendicular to alengthwise direction of the protruding fins 306′. Formation of the firstdummy gate stacks 310′ and the second dummy gate stacks 310″ isdiscussed previously with respect to formation of the dummy gate stacks310 as shown in FIG. 21 , and a detailed description of the same isomitted herein for the sake of brevity.

FIG. 27 illustrates an etching step (referred to as source/drainrecessing hereinafter) performed to etch the portions of the protrudingfins 306′ that are not covered by the dummy gate stacks 310′ and 310″and the gate spacers 38 and selective growth of the epitaxy regions 322a and 322 b (source/drain regions) in the recesses 320. Formation of therecess 320 and the epitaxy regions 322 a and 322 b is discussedpreviously with respect to formation of the recess 320 as shown in FIG.22 , and a detailed description of the same is omitted herein for thesake of brevity.

Contact Etch Stop Layer (CESL) 324 and Inter-Layer Dielectric (ILD) 326are then formed, as shown in FIG. 27 , which illustrates a perspectiveview. Formation of the CESL 324 and the ILD 326 is discussed previouslywith respect to FIG. 22 , and a detailed description of the same isomitted herein for the sake of brevity.

A planarization step such as Chemical Mechanical Polish (CMP) ormechanical grinding using the CMP systems 194 and 202 shown in FIG. 1 or7 and the methods 1000 or 1300 shown in FIG. 10 or FIG. 13 may beperformed to level the top surfaces of the ILD 326, the first and seconddummy gate stacks 310′ and 310″, and the gate spacers 318 with eachother, as shown in FIGS. 29A and 29B. FIGS. 29B and 29C illustratecross-sectional views of the device regions 308 a and 308 b inaccordance with some embodiments. The cross-sectional views combines thecross-sectional view obtained from the vertical plane containing lineB′-B′ in FIG. 29A and the cross-sectional view obtained from thevertical plane containing B″-B″ line in FIG. 29A. If the planarizationstep is performed without using the method 1000 shown in FIG. 10 or themethod 1300 shown in FIG. 13 , some regions where features are notspaced closely together will experience a serious dishing effect(highlighted in FIG. 29C by the dashed circle labeled 344). For example,in some embodiments, the long channel device may suffer from a seriousloading effect resulting from the CMP process

In a subsequent step, as shown in FIG. 30 , silicide region 338,replacement gate stack 328′ and 328″, which includes gate electrodes330′ and 330″ and replacement gate dielectrics 332′ and 332″, andsource/drain contact plugs 336 are formed. Formation of the silicideregions 338, replacement gate stack 328′ and 328″, which includes gateelectrodes 330′ and 330″ and replacement gate dielectrics 332′ and 332″,and the source/drain contact plugs 336 is discussed previously withrespect to FIG. 25 , and a detailed description of the same is omittedherein for the sake of brevity.

Based on the above discussion, it can be seen that the presentdisclosure offers advantages. It is understood, however, that otherembodiments may offer additional advantages, and not all advantages arenecessarily disclosed herein, and that no particular advantages isrequired for all embodiments. One advantage is that the polishing padcan be reconditioned in real-time during polishing the wafer withoutdisposing the conditioning disk. Another advantage is that defectsformed on the surface layer of the wafer during the polishing can bereduced by using the engraved region of the bottom portion of theretainer ring. Still yet another advantage is that production cost canbe saved by using the retainer ring and the conditioning disk made of anon-diamond material.

In some embodiments, a method of using a polishing system includessecuring a wafer in a carrier head, the carrier head including a housingenclosing the wafer, in which the housing includes a retainer ringrecess and a retainer ring positioned in the retainer ring recess, theretainer ring surrounding the wafer, in which the retainer ring includesa main body portion and a bottom portion connected to the main bodyportion, and a bottom surface of the bottom portion includes at leastone first engraved region and a first non-engraved region adjacent tothe first engraved region; pressing the wafer against a polishing pad;and moving the carrier head or the polishing pad relative to the other.

In some embodiments, a method of conditioning a polishing pad includesproviding a polishing pad; providing a slurry including abrasiveparticles and a chemical solution; providing a conditioning disk forconditioning a polishing pad of a chemical mechanical polishing system,in which the conditioning disk has a bottom surface comprising at leastone engraved region and a non-engraved region adjacent to the engravedregion, and the engraved region and the non-engraved region are made ofthe same material; and conditioning the polishing pad using theconditioning disk.

In some embodiments, a chemical mechanical polishing system includes apolishing pad, and a carrier head including a retainer ring to retain awafer proximate to the polishing pad during polishing. A bottom surfaceof the retainer ring has a plurality of protrusions and a substantiallyflat region surrounding the protrusions. The protrusions and thesubstantially flat region are monolithic.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A carrier head of a chemical mechanical polishingsystem, comprising: a housing including a recess; a membrane support,wherein the housing encloses the membrane support; a membrane secured tothe membrane support; and a retainer ring positioned in the recess ofthe housing, wherein the retainer ring includes a plurality of groovesand a first plurality of protrusions, wherein the plurality of grooveshas a longitudinal axis extending from a perimeter of the retainer ringtoward a center of the retainer ring, the first plurality of protrusionsis arranged in rows and columns, and the first plurality of protrusionshas a dimension different from a dimension of the plurality of grooves.2. The carrier head of claim 1, wherein the dimension of the firstplurality of protrusions is smaller than the dimension of the pluralityof grooves.
 3. The carrier head of claim 1, wherein the retainer ringfurther comprises: a vacuum hole placed between two neighbors of theplurality of grooves.
 4. The carrier head of claim 1, furthercomprising: a second plurality of protrusions spaced apart from thefirst plurality of protrusions, wherein the second plurality ofprotrusions is arranged in rows and columns, and the first plurality ofprotrusions and the second plurality of protrusions are placed betweentwo neighbors of the plurality of grooves.
 5. The carrier head of claim4, wherein the second plurality of protrusions has a dimension smallerthan the dimension of the plurality of grooves.
 6. The carrier head ofclaim 4, wherein the retainer ring further comprises: a third pluralityof protrusions disposed in one of the plurality of grooves, wherein thethird plurality of protrusions is arranged in rows and columns.
 7. Thecarrier head of claim 6, wherein the third plurality of protrusions hasa dimension smaller than the dimension of the plurality of grooves.
 8. Achemical mechanical polishing system, comprising: a polishing pad; acarrier head including a retainer ring to retain a wafer proximate tothe polishing pad during polishing; and a conditioning disk placed overa top surface of the polishing pad, wherein the conditioning disk has afirst engraved surface facing the top surface of the polishing pad, thefirst engraved surface is made of a first plurality of non-diamondprotrusions, and the first plurality of non-diamond protrusions isarranged in rows and columns.
 9. The chemical mechanical polishingsystem of claim 8, wherein the conditioning disk further comprises: aplurality of vacuum holes arranged randomly.
 10. The chemical mechanicalpolishing system of claim 8, wherein the conditioning disk furthercomprises: a plurality of vacuum holes arranged concentrically.
 11. Thechemical mechanical polishing system of claim 10, wherein theconditioning disk further comprises: a second engraved surface made of asecond plurality of non-diamond protrusions, wherein the plurality ofvacuum holes is placed between the first engraved surface and the secondengraved surface.
 12. The chemical mechanical polishing system of claim11, wherein the second plurality of non-diamond protrusions is arrangedin rows and columns.
 13. The chemical mechanical polishing system ofclaim 11, wherein when viewed from top, the first engraved surface has adiameter less than a diameter of the conditioning disk.
 14. The chemicalmechanical polishing system of claim 8, wherein the conditioning diskfurther comprises a plurality of non-engraved surfaces having aroughness lower than a roughness of the first engraved surface.
 15. Thechemical mechanical polishing system of claim 14, wherein when viewedfrom top, the plurality of non-engraved surfaces each extends in aradial direction.
 16. The chemical mechanical polishing system of claim14, wherein the conditioning disk further comprises: a vacuum holedisposed on one of the plurality of non-engraved surfaces.
 17. Thechemical mechanical polishing system of claim 14, wherein when viewedfrom top, the plurality of non-engraved surfaces has a circular shape.18. The chemical mechanical polishing system of claim 17, wherein theconditioning disk further comprises: a vacuum hole disposed on one ofthe plurality of non-engraved surfaces.
 19. A chemical mechanicalpolishing system, comprising: a polishing pad; and a carrier headsecuring a wafer, wherein the wafer is between the carrier head and thepolishing pad, and the carrier head comprises: a housing including arecess; a membrane support, wherein the housing encloses the membranesupport; a membrane secured to the membrane support; and a retainer ringpositioned in the recess of the housing, wherein the retainer ringincludes a plurality of grooves, a plurality of bumps interleaved withthe plurality of grooves, and a first plurality of protrusions protrudesfrom one of the plurality of grooves, wherein the first plurality ofprotrusions is arranged in rows and columns.
 20. The chemical mechanicalpolishing system of claim 19, wherein the first plurality of protrusionsis made of a non-diamond material.